Hydrodynamical trigger mechanism for pulsar glitches.

We describe a new instability that may trigger the global unpinning of vortices in a spinning neutron star, leading to the transfer of angular momentum from the superfluid component to the star's crust. The instability, which is associated with the inertial r modes of a superfluid neutron star, sets in once the rotational lag in the system reaches a critical level. We demonstrate that our simple model agrees well with the observed glitch data.